Ocean acidification is a critical issue for the twenty-first century impacting on the health of the ocean, the productivity of fisheries and the conservation and preservation of unique marine environments such as coral reefs. Ocean acidification is an important and potentially dangerous consequence of increasing concentration of anthropogenic carbon dioxide in the Earth's atmosphere. Measurements such as aqueous carbon dioxide partial pressure (pCO2), acidity (pH), total dissolved inorganic carbon (DIC) and total alkalinity (TA) are required to characterize the ocean carbon cycle and such carbon systems.
In anoxic areas (e.g., sediments and stagnant basins) the presence of hydrogen sulfide (H2S) further complicates the carbon system, acting as another component to alkalinity and, thus, affecting the pH and other carbon system parameters. The sulfide system is similar to the carbon system in that it exists in multiple aqueous species (H2S, HS−, and S−2), and the relative abundance of these species is pH dependent. The presence of H2S contributes to the TA, and thus in order to resolve the carbon system in anoxic areas, a third determination of H2S must be also made. Further, H2S is a very reactive chemical that can influence microorganisms that, in turn, influence carbon cycling in aqueous systems.
Devices that sample pore water in sediments require pumps with precisely controlled flow rates, often less than 1 ml/min. Some devices use a variety of piston pumps to draw samples to an analyzer or collection device. However, piston pumps are not dependable to provide a constant flow rate for extended periods of time, especially at low flow rates against varying resistance, and they suffer from pulsation of the flow stream.
Osmotic pumps require no electrical power. They are based on the osmotic pressure differential between seawater and saturated salt solutions. However, osmotic pumps cannot be turned on and off, have extremely low flow rates that cannot be effectively controlled.
In addition, currently used underwater sampling devices cannot perform some analyses in-situ. Rather, the sample must be transported to a remote location for performing further analysis. This leads to the possibility of contamination of the sample or loss of analytes, particularly in the case of highly reactive or volatile species.